Hinode mission delves into the Sun's mysteries

High-resolution images at the edge of the Sun's visible surface, obtained with Solar Optical Telescope aboard Hinode. A radial density filter is applied to show the brighter photosphere and the fainter coronal structures in the same image. This image relates to the paper by Okamoto et al.

New results from the Hinode space mission should help explain some long-standing mysteries of the Sun. ("Hinode" is Japanese for "sunrise.")

The Hinode spacecraft was launched in September 2006 and has been orbiting Earth along a path that keeps it constantly in view of the Sun. The mission is led by the Japan Aerospace Exploration Agency (JAXA), with cooperation from several other space agencies. Some of the first results from the mission appear in a special collection of articles in the 7 December issue of the journal Science.

Mercury transit on the solar disk on Nov. 8, 2006.

One of the big mysteries about the Sun is called the "corona problem." The Sun's surface is about 6,000 Kelvin. That's hot by human standards (water boils at 373 Kelvin on Earth), but it's relatively cool compared to the Sun's atmosphere, also called the corona. The corona is a white-hot 1 million degrees, or even more.

How does the corona get so hot" Several of the Science articles report the discovery of a type of magnetic wave, known as an Alfvén wave, which ripples through the plasma of the Sun's corona. These waves could potentially heat the corona to extreme temperatures by releasing energy as they travel outward from the Sun.

In another study, researchers pinpointed one of the sources of the solar wind, the huge amount of charged particles that the Sun spews into interplanetary space. Earth is protected against the solar wind by its magnetic field, which creates a bubble that the solar wind must flow around.

But sometimes bursts of eruptions of magnetic energy from the Sun cause changes in the solar wind called "space weather" events. These space "storms" can interfere with telecommunications, navigation systems and electric power grids on Earth. Researchers are eager to learn more about the solar wind, in hopes that this information can help them predict or plan for space weather.

One group of Hinode researchers, led by Taro Sakao of JAXA, has now pinpointed a region of the Sun where plasma is continuously flowing into the upper corona. This could be a major source of the solar wind.

These are just a few of the new discoveries that have emerged from the Hinode mission. Researchers expect many more to come.

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